Not applicable.
Not applicable.
The present invention is directed to a process for measuring a total mass of a pressurized fluid flowing through a volume. More particularly, the present invention is directed to an automated fill process for filling vehicles with compressed gas which uses a density calculation combined with a volume flow meter to accurately measure a mass of compressed gas delivered.
Fueling of compressed gas powered vehicles, such as hydrogen (in particular, H2) fuel cell powered vehicles, can be done rapidly by discharging the gas from stored higher pressure vessels into on-board storage vessels. It is imperative that the mass of compressed gas be measured and delivered with an accuracy of better than 1.5% in order to meet the requirements of the various state bureaus of weights and measures. Coriolis effect mass meters are typically used when fueling natural gas vehicles (NGVs). The wide range of flow rates, and the high pressures that are used in this process, make it difficult to identify an appropriate flow meter. In addition, hydrogen vehicles require higher storage pressures than NGVs. As higher supply pressures are used to fill vehicles, it becomes increasingly difficult to find appropriate flow meters that can handle the required flow rates and pressures at the required accuracy. An objective of this invention is to provide an accurate method of mass flow measurement for compressed gas, for example, hydrogen compressed gas, dispensing systems at high pressures.
Installations of compressed gas hydrogen fueling stations have been very limited to date, and none is known to have met national and state standards requirements.
In Canadian Patent No. 1,208,742 (Benner), a system is taught for automatically filling a vehicle with compressed gas. A mass measuring means is used, but its particular function is not described. However, known commercially available NGV dispensers, which claim to meet various national and state standards requirements, typically rely on Coriolis effect meters for mass measurement. Therefore, particularly in light of the fact that this patent issued in 1986, the invention here also is likely to have intended to use Coriolis effect meters.
Turbine meters, in general, are not new. For example, a patent from 1912, U.S. Pat. No. 1,020,127 (Coleman), describes a xe2x80x9cfluid meterxe2x80x9d which is directed to what is now known as a turbine meter. In a turbine meter such as that described in the Coleman patent, a turbine impeller is rotationally mounted in a fluid tight casing. The turbine impeller is rotated by impact or reaction of the fluid to be measured in a passage through a nozzle or nozzles under the pressure head of the fluid. A resistance or load member turns with the turbine impeller and is immersed in and acts on the fluid to be measured in a manner to afford a resistance torque so that the turbine impeller rotates at a moderate rate. The apparatus also includes a registering device, driven by the turbine impeller, which indicates the number of revolutions of the turbine impeller and, consequently, the total volume or quantity of fluid that passes through the apparatus.
U.S. Pat. No. 3,934,473 (Griffo) teaches a major improvement made to the basic turbine meter as described by Coleman above. Here, a second, counter-rotating turbine impeller is added to the meter. The fluid flow meter has two independently counter rotating turbine impellers in which fluid characteristics and/or upstream flow disturbances cause minimal variations in volume flow rate measurements by the meter as a result of fluid dynamic interaction between the impellers. The angular velocities of each of the impellers are sensed in a conventional manner after which the velocity signals are added to indicate a total volume throughput, and/or rate of flow.
In Svedeman et al., xe2x80x9cInterim Report, NGV Fueling Station Technology Program: CNG Dispensing Development Goals,xe2x80x9d Gas Research Institute, Natural Gas Vehicles Technology Research Department, September 1994, the authors compare the potential to use diferent types of meters for filling vehicles with natural gas. Specifically, in Appendix D, a xe2x80x9cReview of Current Gas Metering Technology,xe2x80x9d the authors compare meters having the following technologies: Coriolis effect, weighing systems, thermal, ultrasonic, turbine, vortex shedding, Coanda effect (fluidic meters), differential, criticavsonic nozzles, and positive displacement. These technologies were categorized as having either xe2x80x9cgood,xe2x80x9d xe2x80x9cfair,xe2x80x9d or xe2x80x9cpoorxe2x80x9d potential for measuring compressed natural gas (CNG). The authors give turbine meters, in general, a xe2x80x9cairxe2x80x9d rating for natural gas. The authors state that the pressure capability of turbine meters is adequate and the steady flow accuracy is good for CNG dispensing operations. However, the authors state, two issues required to be resolved are xe2x80x9cthe rangability over which turbine meters are accuratexe2x80x9d and xe2x80x9cthe response of turbine meters to rapid transients.xe2x80x9d In this report, Coriolis meters, pyroelectric meters, and ultrasonic velocity meters were also generally categorized as xe2x80x9cfair,xe2x80x9d while rotary positive displacement meters and sonic nozzle critical flow meters were categorized as xe2x80x9cgood.xe2x80x9d
In White, N., xe2x80x9cNatural Gas for Vehicles, Research and Development Fund, Evaluation of Alternative Dispenser Meters,xe2x80x9d Gas Technology Canada Report, GTC Report NGV 200-8.43, June 1999, turbine flow meters were tested for CNG mass measurement where conditions were similar to a typical CNG fill station. In the testing, the turbine meter accuracy gradually degenerated over a four month test period due to the turbine bearings being slowly contaminated with heavy oil carried over from a compressor. The report also noted that turbine meters are sensitive to low flow rates and, therefore, the flow rates must be verified with proper turbine selection matched with appropriate flow restrictions and cut-off levels. The report also indicated that turbine meters work as well as Coriolis effect meters.
With specific reference to Coriolis meters, the present invention provides for the ability to use a turbine meter. Turbine meters are typically substantially less expensive than Coriolis meters and may also be more accurate.
None of this prior art addresses one of the major limitations of volume flow meters and density calculation. This limitation is the finite response rate of instrumentation. Pressure, temperature and flow rate all can change rapidly during the fill process, as much as 150 bar, 10xc2x0 C., or 10 liters/second, in one second. Since the response rate of these instruments is typically on the order of one second, significant amounts of flow can be missed. The present invention addresses these limitations.
The present invention is directed to a process for measuring a total mass of a pressurized fluid flowing through a conduit. The process includes the steps of measuring a first volume, a first temperature and a first pressure of the pressurized fluid flowing through the conduit during a first timed interval of a sequence of a plurality of timed intervals, calculating a first mass of the pressurized fluid flowing through the conduit during the first timed interval by applying the first temperature and the first pressure to an equation of state to determine a first density and multiplying the first density by the first volume to determine the first mass. The process further includes the steps of measuring a second volume, a second temperature and a second pressure of the pressurized fluid flowing through the conduit during a second timed interval of the sequence of the plurality of timed intervals, calculating a second mass of the pressurized fluid flowing through the conduit during the second timed interval by applying the second temperature and the second pressure to the equation of state to determine a second density and multiplying the second density by the second volume to determine the second mass. Finally, the process includes the step of calculating the total mass of the pressurized fluid through the conduit during the sequence of the plurality of timed intervals by summing the first and second masses of the pressurized fluid flowing through the conduit during the first and second timed intervals.
The process may be for measuring the total mass of a compressed hydrogen gas. The step of calculating a first mass may include calculating at least one of a predicted temperature, a predicted pressure and a predicted volume utilizing at least one value obtained in measuring the first temperature, the first pressure, and the first volume. This would substantially correct any error due to an instrument having a finite response rate.
Finally, the plurality of timed intervals vary may in length.